Measurements of surface vibrations can be made according to a wide variety of techniques. For example, accelerometers can be attached to the surface to be measured to generate an electrical signal responsive to the vibration. In many applications accelerometer measurements and other forms of contact measurements are not practical. The surface to be measured may be damaged or destroyed if a contact device is attached. The weight and stiffness of the device may dampen the vibration, and the vibration measurement is limited to the region on the surface where the device is attached. In addition, contact measurements are not feasible if the surface to be measured is located in an inaccessible space.
Optical vibrometers are often used in applications where physical contact or object location make contact measurements impractical. Typically optical vibrometers use lasers to detect a Doppler frequency shift of light scattered from the surface to characterize the vibration. Examples of non-contact applications for this technique include measurements of the vibration of motors, audio speakers, brakes, hard disk drives, microelectromechanical systems (MEMS), engines, motors, fans and various automotive and aircraft components, and measurements of seismic disturbances. These measurements are limited to applications where there is a direct optical path between the vibrometer and the surface.
What is needed is a sensor system that overcomes the problems and limitations of the techniques described above. The present invention satisfies this need and provides additional advantages.